General Information: The SALSA MLPA Probemixes P251-P252-P253 Neuroblastoma mix 1-3 are a research use only (RUO) assays for the detection of copy number changes of several chromosomal regions that frequently show copy number changes in neuroblastoma tumours.

Neuroblastoma (NB) is a relatively common paediatric cancer that usually occurs sporadically and frequently originates from one of the adrenal glands. Neuroblastoma is characterized by striking clinical heterogeneity, including cases that show spontaneous tumour regression. Neuroblastoma accounts for 6-8% of all cancers in children. Several acquired genetic alterations such as amplification of the MYCN oncogene, deletions of chromosome bands 1p36 and 11q23 and unbalanced gains of 17q regions have been well-characterized and show correlation with tumour behaviour, including response to treatment.

Probemix content: The P251 probemix contains 36 probes in total for chromosomes 1, 3 and 11. The P252 probemix contains 34 probes in total for chromosomes 2 (MYCN region) and 17, and the P253 probemix contains 33 probes in total for chromosomes 4, 7, 9, 12 and 14. In addition, 13 reference probes are included in P251, 15 reference probes are included in P252 and 14 reference probes are included in P253, which all detect different autosomal chromosomal locations which are relatively stable in their copy number in neuroblastoma. However, it should be noted that neuroblastoma karyotypes can harbour multiple numerical and structural aberrations, which can complicate interpretation of these reference probes. Complete probe sequences and the identity of the genes detected by the reference probes is available online (www.mlpa.com).

The P251 probemix contains probes for chromosomes 1, 3 and 11:

• 1p36: A deletion of the 1p36 region is present in 20-40% of NB patients with near-diploid/tetraploid tumours and is often associated with MYCN amplification (in 60% of cases). A probe for 1p36 tumour suppressor gene CHD5 is included.
• 3p21-p22: Deletions on the 3p arm have been described in neuroblastomas, and the RASSF1A gene is a candidate tumour suppressor gene in this region. The presence of 3p deletions appears to correlate with higher age at diagnosis.
• 11q: Deletions of the 11q arm, and in particular 11q23, are common in NB patient samples and associated with higher a disease stage and poor prognosis.

The P252 probemix contains probes for chromosomes 2 and 17:

• 2p24: Amplification of the proto-oncogene MYCN is found in 20-30% of all neuroblastomas. MYCN amplified tumours follow a very aggressive course and are associated with additional structural abnormalities-in particular with loss of 1p, gain of 17q and near-triploidy or -tetraploidy. MYCN amplification is often used for identification of high-risk patients. Additional probes for the nearby NBAS, DDX1 and ALK genes are included.
• 2q33: Loss of 2q33 has been reported in neuroblastomas and has been associated with loss of expression of CASP8.
• 17p: Gains of the 17p probes together with gains of the 17q probes would indicate complete chromosome 17 gains, in contrast to the frequent unbalanced 17q gains that are often associated with translocations. Three probes for TP53 have been included but TP53 mutations and deletions might be rare in neuroblastomas.
• 17q: Unbalanced gain of 17q is present in approximately 50% of patients and is associated with a poor outcome in neuroblastomas. It often results from an unbalanced translocation with 1p or 11q. Gain of 17q, in unbalanced translocations or as part of whole chromosome gain, is seen in 80% of neuroblastomas. Whole chromosome 17 gain is typically seen in near-triploid tumours with favourable prognosis. Please note that triploidy of all chromosomes cannot be detected by MLPA as only relative gains or losses are detected.

The P253 probemix contains probes for chromosomes 4, 7, 9, 12 and 14:

• Partial copy number changes of chromosomes 4, 7, 9, 12 and 14 have been described in neuroblastomas. Probes for CDKN2A and PTPRD on chromosome 9 have been included as CDKN2A is deleted (often homozygously) in many cancer types. The PTPRD gene has also been identified as a candidate tumour suppressor gene in neuroblastoma.

These probemixes contains nine quality control fragments generating amplification products between 64 and 121 nt: four DNA Quantity Fragments (Q-fragments), two DNA Denaturation Fragments (D-fragments), one benchmark fragment, and one chromosome X and one chromosome Y-specific fragment (see table in the product description). More information on how to interpret observations on these control fragments can be found in the MLPA General Protocol and online at www.mlpa.com.